High output fan wheel

ABSTRACT

A high output bent fin type of fan wheel for use in appliances such as but not limited to microwave ovens. The fan wheel is made by single 90-degree bends for each fan blade relative to the flat mounting plate. Unique to fan wheel is the large fan blade surface area in relation to the total area of the metal used in wheel.

This application claims benefit of U.S. Provisional Application Ser. No. 61/755,546 filed Jan. 23, 2013, pursuant to 35 USC §119 (e).

FIELD OF THE INVENTION

This invention relates to fans for appliances, in particular, high output bent fin type of fan wheels.

BACKGROUND OF THE INVENTION

Fan choices for cooking ovens generally include centrifugal, axial, and missed flow blower wheels. Centrifugal fans are further broken down into forward inclined, backward inclined, radial blade and tubular classifications. Axial fans are classified into propeller, tube axial and vane axial. Missed flow fans comprise a group of designs that have an impeller somewhat in between an axial and centrifugal type of design.

Each of these fan designs has well-known advantages and disadvantages over each other when selected for efficiency, horsepower requirement, static pressure generation, housing design, quietness, volume generation, and robustness during design compromises. The construction of centrifugal fans varies greatly. They can be cast, machined, welded, staked from multiple parts or bent from a single sheet of metal.

The fan type most commonly used in appliances both residential and small commercial are the bent fin type. This type of fan wheel is used because of their low cost and ease of manufacture. This invention seeks to get better performance from a bent fin type of fan wheel than is currently available in the market.

SUMMARY OF THE INVENTION

It is an aspect of the invention to provide an improved performing bent fin type of fan wheel for use in appliances such as but not limited to microwave ovens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the high output fan wheel in accordance with the invention.

FIG. 2 is a front view of the high output fan wheel.

FIG. 3 is a side view of the high output fan wheel.

FIG. 4 is a table showing the performance characteristics of the fan wheel in accordance with the invention.

FIG. 5 is a table showing the performance characteristics of a typical prior art fan wheel.

DETAILED DESCRIPTION OF THE INVENTION

Fan wheel 10, shown in FIGS. 1, 2 and 3, is a backward inclined bent fin type of fan wheel. Invention 10 is made by single 90-degree bends for each fan blade 12 relative to the flat mounting plate 20. The fan wheel is made from approximately 0.025-inch thick stainless steel 14. Stainless steel is preferred because stainless steel is a type of a material that is “cold works”, i.e. the material gains strength when bent, in this case, along line 16. This added strength during bending allows the use of the thinner material.

Unique to fan wheel 10 is the large fan blade area surface area 18 in relationship to the total area of the metal used in wheel 10. The total fan blade area is approximately 24.5 square-inches. That is 3.5 square-inches for each blade 12, times 7 blades. The area of the flat mounting surface of mounting plate 20 is only 16.7 square inches. Mounting area 20 does nothing to move air; thus by minimizing it, the use of the metal is optimized. Blades 12 of invention 10 are oriented such that blades 12 are inclined backward at angle 22. This angle is approximately 39 degrees. This large vane area, which has a backward incline allows fan 10 to give increased performance as compared to similar sized fans.

To aid in the balance and stabilization of fan 10, outer ring 24 is positioned on the tips of blades 12. As centrifugal force tends to bend the blades outward, ring 24 helps to keep the blades 12 at the proper 90 degrees. Rings such as ring 24 are well known in art to stabilize the vanes of a fan wheel. In invention 10, the use of ring 24, the backward inclination at angle 22 of blades 12 and the use of stainless steel 14 allow for the use of thinner, less expensive and lighter weight materials. Because of the lightweight construction, ring 24 also serves as an aid to the balance of invention 10. Any vanes 12 that may not be 90 degrees tend to expand tightly into the ring and thus maintain a balanced shape.

FIG. 4 and FIG. 5 show a comparison of invention 10 with a typical prior art fan wheel used today with both fans being used in similar applications. The prior art fan wheel design is a similar folded fin design with a retaining ring. This design is used by Turbochef Technologies of Carrollton, Tex. in thousands of similar sized ovens in use today. The Turbochef wheel has 12 smaller width vanes of similar 1.5 inch height.

Invention 10 uses a lower number of vanes 7, an odd number of vanes 7, a vane with larger area, and an increased backward angle of inclination. The goal of these differences is to create a wheel that exhibits improved performance at similar manufacturing cost and simplicity.

Both fan wheels were tested while attached to the same motor and motor control. This motor and control combination runs the motor speed from minimum to maximum speeds with an applied voltage of 0 to 10 volts to the control. The prior art wheel design (wheel 1, FIG. 5) topped out at a speed of 4260 rpm. This is the maximum speed the selected motor would turn wheel 1. Wheel 10 (wheel 2, FIG. 4) was run with the same motor and motor control and reached a maximum speed of 6700 rpm. This data shows that invention 10 can spin at a much higher speed, thus delivering much greater air flow with the same input power.

Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the preferred embodiments contained herein. 

What is claimed is:
 1. A centrifugal fan for an oven having a fan motor, wherein said fan is made from a single sheet of metal using a bent fin-type plurality of fan blades, said fan comprising: a mounting plate having a plate surface area, wherein said mounting plate is used to connect said fan to the fan motor; a plurality of fan blades wherein each blade has a tip and wherein said plurality of fan blades having a fan blade surface area, wherein the fan blade surface area is greater than the plate surface area of said mounting plate; and wherein each of said plurality of fan blades is made by a single 90 degree bend relative to said mounting plate; and wherein each blade of said plurality of fan blades is inclined backward at a predetermined angle.
 2. The centrifugal fan of claim 1 wherein the predetermined angle is 39 degrees.
 3. The centrifugal fan of claim 1 further comprising an outer ring attached to the tips of said plurality of fan blades in order to stabilize each blade at the proper 90 degrees.
 4. The centrifugal fan of claim 1 is made from stainless steel which allows for thinner, less expensive and lighter weight materials.
 5. The centrifugal fan of claim 1 wherein the number of said fan blades is an odd number.
 6. The centrifugal fan of claim 5 where the odd number of blades is
 7. 